Engine systems on vehicles, such as hybrid electric vehicles (HEV) and vehicles configured for idle-stop operations, may be configured with a laser ignition system. In addition to initiating cylinder combustion, the laser ignition system may be used during engine starting to accurately determine the position of a piston in each cylinder, enabling an appropriate cylinder to be selected for a first combustion event. As such, this improves the engine's ability to restart. The laser ignition device may be continually operated at high energy intensity to ensure that each combustion event has good combustion of the air-fuel mixture. However, since the laser ignition system uses energy from a vehicle system battery, frequent firing of the laser can deplete the battery. In hybrid vehicles, this can adversely affect vehicle fuel economy.
One example approach for improving fuel economy, when using a laser ignition system, is shown by Woerner et al. in US 2013/0098331. Therein, optimum burn-through of a cylinder air-fuel mixture is achieved by irradiating an ignition location inside a pre-combustion chamber with a plurality of laser ignition pulses temporally offset from one another. This allows a flame core generated in the pre-combustion chamber to be advantageously used to ignite the air-fuel mixture of the pre-combustion chamber as well as the main combustion chamber, thereby reducing overall laser ignition usage.
However, the inventors herein have recognized potential issues with such an approach. As one example, the approach may not be applicable in engine systems where each combustion chamber is not coupled to a corresponding pre-combustion chamber. As another example, if the flame core in the pre-combustion chamber is not generated correctly, in addition to the laser energy expended in generating the pre-combustion chamber flame core, further laser energy may need to be expended to generate a combustion chamber flame core. As such, this may increase battery charge consumption and degrade fuel economy.
In one example, some of the above issues may be addressed by an engine method comprising, dynamically adjusting a laser intensity of an engine laser ignition device during a cylinder ignition event based on a monitored cylinder flame quality. In this way, the laser intensity of the laser ignition system can be reduced until flame quality is affected to improve battery consumption.
For example, an engine in a hybrid electric vehicle may be configured with a laser ignition system including a battery-operated laser ignition device for igniting an air-fuel mixture and a photodetector for monitoring a flame quality inside each cylinder. Over a drive cycle, the laser intensity of the laser ignition device may be reduced (e.g, step-wise) over each ignition event while the photodetector is used to monitor the flame quality at each corresponding cylinder combustion event. The step-wise reduction may be based on, for example, engine load, cylinder head temperature, and combustion air-fuel ratio. The photodetector may include, for example, an infrared sensor and/or CCD camera for inferring a flame quality based on the peak in-cylinder temperature achieved during cylinder combustion following each ignition event. If the peak in-cylinder temperature achieved is lower than a threshold, it may be determined that good combustion did not occur (e.g. insufficient combustion occurred). In response to a threshold number of consecutive degraded flame events (e.g., 1-2 consecutive degraded flame events), it may be inferred that the laser energy is too low for combustion and the intensity of the laser ignition device may be increased to improve the combustion. Then, the reduction of laser intensity may be reiterated, for example, with a smaller drop in laser intensity at each ignition event. This allows for optimal laser energy usage.
In this way, laser ignition intensity may be dynamically adjusted over a vehicle drive cycle to reduce battery consumption. By reducing the laser ignition intensity as much as possible without affecting flame quality, laser energy consumption is reduced. By using a closed-loop adjustment of laser intensity based on flame quality, rather than an open-loop adjustment that over-compensates laser energy to always guarantee high flame quality, significant laser energy wastegate is reduced. As such, this reduces battery consumption and improves fuel economy in a hybrid vehicle system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.